This media tests for the ability of an organism to break down and use a
vegetable lipid (tributyrin) present in the agar plates. If an organism
is able to secrete lipase the lipid can be hydrolysed. The media usually
contains spirit blue or methylene blue as an indicator. Use of the lipid
can be observed as a zone of clearing around areas of growth. The zone
has to be transparent for the test
to be considered positive; color changes are not considered to be positive.